VMD-L Mailing List

From: JC Gumbart (gumbart_at_ks.uiuc.edu)
Date: Sun Jan 20 2013 - 13:16:33 CST

The energies and distances are written out to the log file at each step (as far as I know they still are???). You can use the charge optimization log plotter (COLP) to track their progress over the optimization procedure.

The 1.2-1.5 is taken from the CGenFF 2009 paper: "Typically,the force field should overestimate gas phase dipole moments by 20 to 50% to be relevant for the bulk phase,".

After spending quite an amount of time on force-field parametrization, one thing that becomes apparent is that the rules aren't as precise or deterministic as we would hope! So don't obsess over 1.4 vs. 1.3, for example, because you'll never actually be able to satisfy all constraints simultaneously anyway.

On Jan 19, 2013, at 8:12 PM, ehsan zahedinejad wrote:

> Dear VMD users,
>
> In the charge optimization step of fftk, three factors including "dipole moment", "water interaction energy and distance" are the target data. The new fftk version writes out the dipole ratio of QM to MM but not energy and distance. How can we be informed about these targets in optimization to be sure they are fulfilled by optimization procedure?
>
> The second important matter is the ratio of dipole moments. In the tcl file of charge optimization a ratio between 1.2-1.5 is considered as an acceptable target. But CHARMM general force field tutorial says dipole moment of MM force field should be 30% higher than QM level (MP2). Is that still OK to have dipole moment 20-50% higher than MM dipole moment? For example what if my ratio is 1.4?
>
> And thanks for this amazing tool,
>
>
> Cheers,
> Ehsan.